Cryptology ePrint Archive: Report 2005/383

Key Mixing in Block Ciphers through Addition modulo $2^n$

Debdeep Mukhopadhyay and Dipanwita RoyChowdhury

Abstract: The classical technique to perform key mixing in block ciphers
is through exclusive-or (exor). In this paper we show that
when the $n$-bit key is mixed in a block cipher of size $n$
bits via addition modulo $2^n$, the bias of the linear approximations
falls exponentially fast. Experimental results have been provided
to show that such a scheme cannot be cryptanalyzed
using Linear Cryptanalysis.